The invention relates to electric appliances, electric lamps and other electrically operated (current-consuming) devices which can be found in a kitchen, in a bathroom, in a basement, in a garden and/or elsewhere to be operated by completing their electric circuits. More particularly, the invention relates to improvements in apparatus or systems for protecting electrically operated devices from damage which could develop as a result of the influence of current-conducting moisture, e.g., in response to penetration of water into an electrically operated device in a basement, cellar, bathroom, kitchen or garden.
European patent application No. 0 088 390 discloses a protecting apparatus which employs a moisture sensor serving to generate signals which are processed and utilized to prevent the development of shocks, to prevent short circuiting of an electrically operated device and/or to prevent any other damage to the device and/or injury to the person or persons nearby. The moisture detector includes a probe in the form of an open twin electric conductor which cannot be touched by a person manipulating the electrically operated device (hereinafter called consumer for short). The probe changes its electrical impedance in the presence of moisture and is connected with the input of an ignition-circuit which contains a semiconductor switch. The arrangement is such that the switch is fired (closed) when the impedance of the probe changes as a result of contact with moisture. Closing of the semiconductor switch entails the flow of electric current to initiate automatic opening of a mechanical switch in circuit with the consumer and with the energy source. The contacts of the mechanical switch are maintained in engagement with one another by a mass which is supposed to melt under the direct or indirect action of heat developing in response to closing of the semiconductor switch and the resulting flow of electric current through the conduit including the mechanical switch. In one embodiment of the just outlined apparatus, the mechanical switch is a single-pole switch which opens in response to melting of a wire. To this end, the mechanical switch comprises a base of insulating material, a rigid contact which is anchored in the base, a mobile contact which is also anchored in the base, a resilient yoke, and a so-called elastic or spiral spring. Such mechanical switches are also called spiral or elastic spring switches. A spiral switch closes in response to depression of the yoke and opens when the yoke is free to move upwardly. The forward end of the prestressed yoke is provided with an injection molded or extruded plastic anchor for a wire having a low melting point and being connected with two pins. One conductor of the circuit including the energy source and the consumer includes the pins, and the other conductor of such circuit includes the yoke and the spiral spring. The dimensions of the wire must be selected in such a way that the wire does not melt in response to the flow of rated current for the consumer, i.e., that such current can flow without melting the wire which would result in opening of the spiral spring switch.
The just described conventional apparatus exhibit the advantage that all poles of the switch are disconnected from the energy source in response to penetration of water or any other current-conducting moisture into the range of the moisture detecting probe before a person is affected by electric current, e.g., by contacting the body of water which has penetrated into the consumer. The arrangement is such that the mechanical switch irreversibly interrupts the flow of electric current between the energy source and the consumer. Consequently, a consumer which has been affected by moisture cannot be set in operation without an extensive delay. Another drawback of such apparatus is their complexity and high cost as well as that the reaction time is too long.